Can someone clarify the function of the nRESET pin on the expansion
connector. The description in the HRM suggests the pin is low to reset
the expansion board during power up, and then after power up, the
expansion board may bring the pin low to reset the system.
I'm guessing this is some kind of wired-or line, where low means
reset, and multiple sources can bring the line low to force a reset?
The reset line is an open collector line. If you press the reset button it pulls it low. If you ground the reset line from the expansion connector, it will go low. On power up, the TWL4030 forces the line low for the power on reset. The reset line on the expansion connector is the same exact line that connects to the processor. You can check the schematic for further details in the System Reference Manual.